The El’gygytgyn impact structure, Siberia: Impactites from a mid-size impact structure in volcanic target rocks
The El’gygytgyn crater in Chukotka (Russia) is one of the best-preserved complex impact structures, worldwide. At ca. 3.6 million years ago a projectile of probably chondritic composition hit into an at least several hundred-meter-thick sequence of different, predominantly felsic, volcanic rocks. Th...
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| Other Authors: | , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
2017
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| Online Access: | https://refubium.fu-berlin.de/handle/fub188/1943 https://doi.org/10.17169/refubium-6145 https://nbn-resolving.org/urn:nbn:de:kobv:188-fudissthesis000000105365-6 |
| Summary: | The El’gygytgyn crater in Chukotka (Russia) is one of the best-preserved complex impact structures, worldwide. At ca. 3.6 million years ago a projectile of probably chondritic composition hit into an at least several hundred-meter-thick sequence of different, predominantly felsic, volcanic rocks. These belong to the Upper Cretaceous Ochotsk Chukotka Volcanic Belt (OCVB). In addition to the dominant rhyolitic/rhyodacitic ignimbrites, there are also layers of andesitic to basaltic composition. Some time after crater formation (some thousand to fifty thousand years), a lake was established in the impact structure and accumulation of lake sediments started. The El’gygytgyn impact structure is not only a special crater in terms of its lithologies, but it provides with its undisturbed lacustrine sedimentation a great climate archive for the entire Quaternary era. These were also the main reasons for the deep drilling of the structure by the International Continental Scientific Drilling Program (ICDP) in 2009. Of the four drill holes achieved, borehole D1c is the deepest with ~520 m and yielded approximately 200 m of impact-related rocks from the flank of the collapsed central uplift. These rocks have been accurately examined during this thesis work, focusing on the lithostratigraphy, the distribution of shock effects within the drilled sequence, and on the development of suevitic breccias and impact-induced melt. The drilled rocks can be divided into four units. The uppermost 12 meters (316-328 meters below lake floor = mblf) are reworked suevite and contain unshocked to strongly shocked clasts of various volcanic rocks (basalt to rhyolite). Furthermore, in this unit occurs the comparatively largest proportion of impact-generated melt as several centimeter large melt particles or tiny (<1 mm) glass spherules. The fine-grained matrix consists mainly of the same material as the lithic clasts and is enriched with finest- grained ash particles from the collapsed ejecta plume and with clay and fine sand from the ... |
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